1. Field of the Invention
The present invention relates generally to a method and an apparatus for deciding a Channel Quality Indicator (CQI) in a wireless communication system, and in particular, to a method and an apparatus for deciding a CQI using a genetic algorithm (GA) in a wireless communication system.
2. Description of the Related Art
High Speed Downlink Packet Access (HSDPA) technology is in an evolution progress of asynchronous International Mobile Telecommunications (IMT)-2000 standards. The HSDPA is an access scheme which defines a transport channel such as a High Speed-Downlink Shared CHannel (HS-DSCH), and control channels such as a High Speed-Shared Control CHannel (HS-SCCH) and a High Speed-Dedicated Physical Control CHannel (HS-DPCCH) in order to support a high-speed downlink packet data service. The definition is given to allow the transport channel and the control channels to operate in Frequency Division Duplexing (FDD) and Time Division Duplexing (TDD) of Release 5 of a Universal Mobile Telecommunications System (UMTS). The HSDPA is also a main feature of Release 5 standards of a 3rd Generation Partnership Project (3GPP). In particular, HSDPA is recognized as a system which efficiently provides an information provider (IP) multimedia service which has dramatically improved a transfer rate and recently come into the spotlight.
A structure of a system using an HSDPA protocol is modified to position a scheduling function and most radio resource control functions in a Node B (base station) close to a wireless access interface so as to efficiently use link adaptation techniques such as Adaptive Modulation and Coding (AMC) or Hybrid Automatic Repeat reQuest (HARQ) adopted in HSDPA. For this purpose, a sub-layer called a Medium Access Control high speed (MAC-hs) layer is positioned at a lowest part of a MAC layer to function to select a Modulation and Coding Scheme (MCS) fit for fading channel environments or schedule data.
2 ms(=3 slots) corresponding to ⅕ of an existing 10 ms(=15 slots) frame is determined as a sub-frame and defined to be a size of a Transmission Time Interval (TTI) in order to effectively cope with momentary variations of a channel. Also, a User Equipment (UE) measures a received shared pilot channel and transmits a Channel Quality Indicator (CQI) reflecting the received shared pilot channel through an HS-DPCCH in order to assist the Node B to determine a state of the channel. The Node B transmits packet data to the UE in order to increase a throughput of the channel, wherein AMC using a modulation scheme and a channel coding rate varying with variations of the channel indicated by the CQI is applied to the packet data. The UE uses HARQ to transmit whether the packet data has been successfully received, as an acknowledgement (ACK) or a negative ACK (NACK) through the HS-DPCCH to the Node B. Here, a size of the transmitted packet data is determined according to the modulation scheme and the channel coding rate. Thus, a downlink data processing speed is determined according to a CQI value.
In the prior art as described above, a 3GPP spec recommends that a CQI value be set so that a block error rate (BLER) does not exceed 0.1 (10%). Thus, solution enterprises substantially realize CQIs using different methods, which are rarely recognized as unique schemes and open to the public. The methods are only to decide central values of CQI distributions as the CQIs with reference to BLERs depending on the CQI distributions. Here, since CQI values vary with ranges of determining the CQI distributions and measuring the BLERs, it is difficult to fully understand unique methods of deciding CQIs. The BLERs necessary for deciding the CQIs must be kept under 10% but are substantially difficult to satisfy this condition. This is because probability values using the central values of the CQI distributions, not individual values, are determined as the CQIs. Also, when data is coded using a turbo decoder, the BLERs suddenly change. Thus, the BLERs are determined within a range between 25% and 30%.
Accordingly, a method and an apparatus for ensuring a BLER of less than 10% and rapidly deciding a CQI as an individual value are required.